The invention relates to liquid adjuvants, in the form of microemulsions, which may be combined with agricultural chemicals to improve the efficacy thereof.
Agrochemicals such as, for example, biocides, herbicides, insecticides and even fertilizers contain organic compounds which are insoluble or poorly soluble in water. In order to convert these agrochemicals into a form in which they are easy to handle by the user, they are often marketed as concentrated solutions in suitable organic solvents, for example alkyl benzene. Before use, these solutions have to be diluted to their required concentrations. However, the use of these organic solvents is undesirable for economic reasons and above all for ecological reasons. Accordingly, there is a need for water-based concentrates of the agrochemicals in question.
Generally, microemulsions are isotropic, thermodynamically stable mixtures comprising oil, water and an emulsifier, and, optionally, additives which may include alcohols and electrolytes. The emulsifier commonly comprises alkoxylated non-ionic surfactants, e.g., ethylene oxide, propylene oxide and mixtures thereof, which will prevent the microemulsion from breaking down to separated oil and water based phases within a relatively limited temperature range.
Microemulsions of this type have served the pesticide industry in the form of ready to use adjuvant products for use with agricultural chemicals (agrochemicals) for a number of years. The fine droplet size (typically as small as about 100 nm) of these emulsions results in clear, transparent products with long shelf lives. The water component of the microemulsion typically replaces a significant portion of the hydrocarbon solvents normally used with hydrophobic agrochemical concentrates, resulting in environmentally friendly formulations. However, these microemulsions contain a large amount of surfactants based on ethylene and propylene oxide block copolymers, which are poorly biodegradable and phytotoxic to plants. Furthermore, these block copolymers possess a cloud point, a well known property of block copolymers and nonionic surfactants which is the result of the surfactant becoming less soluble with increasing temperature; the temperature at which the appearance of a second phase is observable is the “cloud point” (see Kirk Othmer's Encyclopedia of Chemical Technology, 3rd ed. Vol. 22, pp. 360-361 (John Wiley & Sons, 1983)). Accordingly, if the temperature of the microemulsion reaches the cloud point, the microemulsion will be unstable.
U.S. Pat. No. 6,255,253 to Foerster et al. discloses a microemulsion formulation including water, an emulsifier, and an oil phase comprising a water-insoluble agrochemical, i.e., the oil droplets in the microemulsion comprise the agrochemical component. In this type of mixture the water-insoluble agrochemicals are put into a microemulsion with the emulsifier(s) and water so that they are essentially ready for use, though they are typically diluted before being applied in the field.
However, it is often convenient to maintain separate stocks of agrochemical and adjuvant and combine them, with additional water, just prior to their application in the field. Further, it is preferable for an adjuvant to be suitable for use with a number of different agrochemicals which may be chosen by the user, not just oil based agrochemicals.
Accordingly, it would be advantageous to have an ecologically safe, temperature stable microemulsion which may be mixed with water-soluble, substantially water-soluble, water-insoluble, or substantially water-insoluble agrochemicals shortly before their application and which will increase the efficacy thereof.